An example of various types of control systems for rotary machines is disclosed in Japanese Patent Application Publication No. 2008-228476. The Patent Application Publication discloses a control system for a three-phase motor as an example of rotary machines. The control system includes an inverter for converting DC (Direct Current) power to AC (Alternating Current) power. The control system is designed to correct the output voltage of the inverter, which is proportional to the rotational speed of the three-phase motor, such that the peak value of a current, which flows in the three-phase motor and is fed back to the control system, becomes a predetermined value.